Growth and Applications of Horizontally Aligned Single-walled Carbon Nanotubes

Abstract

Single-walled carbon nanotube (SWNT) is a rolled-up graphene. SWNT is one of the most important materials in nano-technology and many SWNT applications have been proposed. Especially, the field-effect-transistors (FETs) with SWNT-channels attract much attention. For the fabrication of such SWNT electric devices, alignment and position control of SWNTs is important. Additionally, pure semiconducting SWNT arrays is needed for SWNT-FETs with high performance. Here, we present the growth of horizontally aligned SWNTs (HASWNTs) and fabricate pure-semiconducting SWNT-FETs using a selective removal technique. We used iron nanoparticles as the catalyst, ethanol vapor as the carbon source for SWNT growth. HA-SWNTs are synthesized on single-crystal (R-cut) quartz substrates. In advance, the R-cut quartz substrates were annealed at 900 ◦C in air for 12 h and iron was deposited in a strip pattern. The sample was heated up in Ar/H2 (3%) mixture gas. At 800 ◦C, ethanol vapor was introduced together with Ar/H2 (3%) gas and CVD growth was performed. The SWNTs were aligned along the direction of the x-axis of R-cut quartz. The density of HASWNTs depended on CVD conditions and the partial pressure of ethanol vapor was key point. HA-SWNTs were analyzed by scanning electron microscopy (SEM) and scanning Raman scattering spectroscopy. For selective removal of metallic SWNTs, we used thermal-lithography technique and an organic film-assisted electrical breakdown method. For thermal-lithography technique, HA-SWNTs were covered with molecular glass thin film and applied electric voltage to HA-SWNTs. Only metallic SWNTs were Joule-heated and they became exposed owing to thermocapillary flow of molecular glass. By etching exposed metallic SWNTs, the SWNT-FETs with higher on/off ratio could be obtained. In the case of the electrical breakdown method, metallic SWNTs covered with films were Joule-heated. The heated parts of metallic SWNTs was oxidized and removed. The cover films significantly extended the removed length of metallic SWNTs.